Memory enjoys a significant position in the semiconductor market, 10% of which is occupied by dynamic random access memory (DRAM) and flash alone. With the gradual popularity of portable electronic devices, a growing market for non-volatile memory can be expected, coupled with increasingly high requirements of consumers for the capacity, speed and etc. of memory. As a mainstream non-volatile memory, flash technology has encountered the bottleneck. The technical weakness becomes more highlighted with the development of integrated circuits. Limitations such as low speed, high write voltage and limited number of cycles have directly restricted further application of flash technology. Therefore, it is urgent to develop a novel memory technology to replace it so as to maintain the direction of development toward scaling down to small sizes for memory technology.
Phase change memory (PCM) technology, emerging in recent years and enjoying extensive application prospect, is a new kind of memory technology where phase change material is used as the storage medium; recently it is a hot point in memory research and is regarded as the most promising one to become the mainstream memory of the next generation. Since most of the phase change materials comprise chalcogen elements, they are also know as chalcogenide random access memory, considered as the semiconductor memory characterized by high speed, high density, low power consumption, high reliability, low cost and etc. Data storage of chalcogenide random access memory is realized by the reversible phase change between amorphous and polycrystalline states when phase change material is activated by applying energy, wherein the chalcogenide has high resistance in amorphous state and low resistance in polycrystalline state, thus PCM utilizes the resistance difference between the high and low resistance states to store “0” and “1”.
Ge2Sb2Te2 is a typical phase change material used for PCM, but it is found in actual applications that, due to great change of density and poor crystallization speed (about hundreds of ns generally) of Ge2Sb2Te2 material during phase change, the erase and write speed and the device reliability are influenced; furthermore, low crystallization temperature of about 160° C. makes it difficult to be used under high temperature conditions. Therefore, Ge2Sb2Te2 is not a prefect phase change material, especially for applications in certain special conditions.
To sum up, it is an urgent issue at present to develop novel phase change materials that can help devices simultaneously possess multiple advantages such as high speed, high reliability, high density, good thermal stability and low cost, or that demonstrate outstanding performance in certain aspects.